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| Author | : Conrad Pawel Koziol |
| Publisher | : |
| Total Pages | : |
| Release | : 2018 |
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| ISBN | : |
| Author | : W. Tad Pfeffer |
| Publisher | : Frontiers Media SA |
| Total Pages | : 160 |
| Release | : 2018-11-08 |
| Genre | : |
| ISBN | : 2889456196 |
Melt takes place where the surface of glaciers or ice sheets interacts with the atmosphere. While the processes governing surface melt are fairly well understood, the pathways of the meltwater, from its origin to the moment it leaves a glacier system, remain enigmatic. It is not even guaranteed that meltwater leaves a glacier or ice sheet. On Greenland, for example, only slightly more than 50% of the meltwater runs off. The remainder mostly refreezes within the so-called firn cover of the ice sheet. This eBook contains 11 studies which tackle the challenge of understanding meltwater retention in snow and firn from various angles. The studies focus both on mountain glaciers and on the Greenland ice sheet and address challenges such as measuring firn properties, quantifying their influence on meltwater retention, modelling firn processes and meltwater refreezing as well as unravelling the mechanisms within the recently discovered Greenland firn aquifers.
| Author | : C.J. van der Veen |
| Publisher | : CRC Press |
| Total Pages | : 407 |
| Release | : 2013-03-26 |
| Genre | : Science |
| ISBN | : 1439835667 |
Measuring, monitoring, and modeling technologies and methods changed the field of glaciology significantly in the 14 years since the publication of the first edition of Fundamentals of Glacier Dynamics. Designed to help readers achieve the basic level of understanding required to describe and model the flow and dynamics of glaciers, this second edition provides a theoretical framework for quantitatively interpreting glacier changes and for developing models of glacier flow. See What’s New in the Second Edition: Streamlined organization focusing on theory, model development, and data interpretation Introductory chapter reviews the most important mathematical tools used throughout the remainder of the book New chapter on fracture mechanics and iceberg calving Consolidated chapter covers applications of the force-budget technique using measurements of surface velocity to locate mechanical controls on glacier flow The latest developments in theory and modeling, including the addition of a discussion of exact time-dependent similarity solutions that can be used for verification of numerical models The book emphasizes developing procedures and presents derivations leading to frequently used equations step by step to allow readers to grasp the mathematical details as well as physical approximations involved without having to consult the original works. As a result, readers will have gained the understanding needed to apply similar techniques to somewhat different applications. Extensively updated with new material and focusing more on presenting the theoretical foundations of glacier flow, the book provides the tools for model validation in the form of analytical steady-state and time-evolving solutions. It provides the necessary background and theoretical foundation for developing more realistic ice-sheet models, which is essential for better integration of data and observations as well as for better model development.
| Author | : Laura A. Stevens |
| Publisher | : |
| Total Pages | : 220 |
| Release | : 2017 |
| Genre | : Glaciers |
| ISBN | : |
Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia–Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss.
| Author | : Bo Qu |
| Publisher | : Springer |
| Total Pages | : 93 |
| Release | : 2014-10-09 |
| Genre | : Science |
| ISBN | : 3642544983 |
Arctic marine ecosystems are largely impacted by changes associated with global warming. The sea ice in Greenland Sea plays an important role in regional and global climate system. The book investigate the relationships between phytoplankton biomass, measured using remotely sensed chlorophyll-a (CHL), aerosol optical depth (AOD) and sea-ice cover (ICE) in the Greenland Sea (20°W-10°E, 65-85°N) over the period 2003-2012. First hand Satellite data was used to do correlation analysis. Enhanced statistics methods, such as lag regression method and cointegration analysis method are used for correlation and regression analysis between 2 variables (up to 3 variables). ARMA model was used to prediction time series in the future 3 years. The book not only gives outline of ecosystem in Greenland Sea, how the ice impact to the local ecosystems, but also provides valuable statistical methods on analysis correlations and predicting the future ecosystems.
| Author | : Vena Chu |
| Publisher | : |
| Total Pages | : 221 |
| Release | : 2015 |
| Genre | : |
| ISBN | : |
The current need for forecasting Greenland Ice Sheet contributions to global sea level rise is complicated by the lack of understanding of ice sheet hydrology. The proportion of meltwater contributing to sea level rise, as well as the pathways transporting meltwater on, through, and out of the ice sheet, are not well understood. Remote sensing of hydrologic dynamics in combination with small-scale fieldwork allows examination of broad spatial and temporal trends in the Greenland hydrologic system responding to a changing climate. This dissertation reviews the current state of knowledge on Greenland Ice Sheet hydrology, and examines three components of the Greenland hydrologic system: (1) fjord sediment plumes as an indicator of meltwater output, (2) supraglacial streamflow as an indicator of meltwater input to the ice sheet, and (3) moulin distribution and formation as a mechanism diverting meltwater from the surface of the ice sheet to the bed. Buoyant sediment plumes that develop in fjords downstream of outlet glaciers are controlled by numerous factors, including meltwater runoff. MODIS retrievals of sediment plume concentration show a strong regional and seasonal response to meltwater production on the ice sheet surface, despite limitations in fjords with rapidly calving glaciers, providing a tool for tracking meltwater release to the ocean. Summertime field observations and high-resolution satellite imagery reveal extensive supraglacial river networks across the southwestern ablation zone transporting large volumes of meltwater to moulins, yet these features remain poorly mapped and their discharges unquantified. A GIS modeling framework is developed to spatially adapt Manning's equation for use with high-resolution WorldView-2 imagery to map supraglacial river discharge. Moulins represent connections between surface meltwater on the Greenland ice sheet and subglacial drainage networks, where increased meltwater can enhance ice sliding dynamics. A new high-resolution moulin dataset in western Greenland created from WorldView-1/2 imagery in the 2012 record melt year is used to assess moulin distribution and formation. Moulin locations show a significantly different distribution compared to geospatial variables in the entire study area, with moulins forming in areas of thinner ice, higher velocity and extensional strain rate, as well as lower surface elevation and slope, and higher bed elevation and slope.
| Author | : Adam Igneczi |
| Publisher | : |
| Total Pages | : |
| Release | : 2018 |
| Genre | : |
| ISBN | : |
| Author | : Kristin Poinar |
| Publisher | : |
| Total Pages | : 152 |
| Release | : 2015 |
| Genre | : Glaciers |
| ISBN | : |
As the climate has warmed over the past decades, the amount of melt on the Greenland Ice Sheet has increased, and areas higher on the ice sheet have begun to melt regularly. This increase in melt has been hypothesized to enhance ice flow in myriad ways, including through basal lubrication and englacial refreezing. By developing and interpreting thermal ice-sheet models and analyzing remote sensing data, I evaluate the effect of these processes on ice flow and sea-level rise from the Greenland Ice Sheet. I first develop a thermal ice sheet model that is applicable to western Greenland. Key components of this model are its treatment of multiple phases (solid ice and liquid water) and its viscosity-dependent velocity field. I apply the model to Jakobshavn Isbræ, a fast-flowing outlet glacier. This is an important benchmark for my model, which I next apply to the topics outlined above. I use the thermal model to calculate the effect of englacial latent-heat transfer (meltwater refreezing within englacial features such as firn and crevasses) on ice dynamics in western Greenland. I find that in slow-moving areas, this can significantly warm the ice, but that englacial latent heat transfer has only a minimal effect on ice motion (10%). By contrast, in fast-flowing regions, which contribute most (60%) of the ice flux into the ocean, evidence of deep englacial warming is virtually absent. Thus, the effects of englacial latent heat transfer on ice motion are likely limited to slow-moving regions, which limits its importance to ice-sheet mass balance. Next, I couple a model for ice fracture to a modified version of my thermal model to calculate the depth and shape evolution of water-filled crevasses that form in crevasse fields. At most elevations and for typical water input volumes, crevasses penetrate to the top ~200–300 meters depth, warm the ice there by ~10°C, and may persist englacially, in a liquid state, for multiple decades. The surface hydrological network limits the amount of water that can reach most crevasses. We find that the depth and longevity of such crevasses is relatively robust to realistic increases in melt volumes over the coming century, so that we should not expect large changes in the englacial hydrological system under near-future climate regimes. These inferences put important constraints on the timescales of the Greenland supraglacial-to-subglacial water cycle. Finally, I assess the likelihood that higher-elevation surface melt could deliver water to regions where the bed is currently frozen. This hypothetical process is important because it could potentially greatly accelerate the seaward motion of the ice sheet. By analyzing surface strain rates and comparing them to my modeled basal temperature field, I find that this scenario is unlikely to occur: the conditions necessary to form surface-to-bed conduits are rarely found at higher elevations (~1600 meters) that may overlie frozen beds.
| Author | : Lei Yang |
| Publisher | : |
| Total Pages | : 160 |
| Release | : 2007 |
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| ISBN | : |
The co-variability of glacier ice discharges and climate variability is also examined by using Polar MM5 V1 modeled summer temperature and April-September Positive Degree Day (PDD) anomalies. Ice discharges from south Greenland glaciers are found to be sensitive to temperature change. Based on sensitivities of ice discharge to melt index anomalies, time series of total ice discharge from 28 major glaciers since 1958 are modeled. The global sea level rise contribution from Greenland ice sheet during past 50 years is estimated be ∼0.6 mm yr-1 in average.
| Author | : Celia Trunz |
| Publisher | : |
| Total Pages | : 344 |
| Release | : 2021 |
| Genre | : |
| ISBN | : |
In the ablation zone of land terminating sectors of the Greenland Ice Sheet (GrIS), water pressures at the bed control ice motion variability on diurnal and seasonal timescales. During the melt season, large volumes of surface meltwater access the ice-bed interface through moulins.Moulins are large vertical shafts that connect the supraglacial and subglacial drainage systems. Moulins form when a crevasse intersects a surface meltwater source that can drive hydrofracture to the bed of the ice sheet. Upon reaching the bed, meltwater can establish and sustain an efficient, channelized drainage system. Due to the technical impossibility of physically exploring underwater passages beneath the GrIS, the subglacial drainage system must be studied through geophysical methods. To date, measurements of water level variability within moulins and boreholes have proved to be critical for constraining models. However, direct hydrologic measurements from the GrIS are sparse, due to the remoteness and harsh conditions of the ice sheet. The work presented in this dissertation combines simple physically based mathematical models with direct measurements from the ablation portion of Sermeq Avannarleq, in west Greenland to advance our understanding of the influence of moulin geometry and life span on glacier dynamics. In Chapter 2, I investigate the moulin life cycle within several neighboring surface catchments within the GrIS ablation zone. A combination of remote sensing and ground observations of moulin locations over two to three years reveals an annual pattern of systematic formation and abandonment of moulins after they are advected down-glacier.In Chapter 3, I use a modified single conduit model to explore the role of moulin shape and size on hydraulic head variability within moulins. This model shows that only the englacial storage capacity within the range of water level fluctuations affects the oscillation range of moulin hydraulic head, which controls subglacial channel water pressure dynamics. Further, the model shows that depth-varying changes in englacial water storage control the temporal shape of the head oscillations. Finally, in Chapter 4, I simulate the moulin water level variability in a moulin we instrumented in 2017-2018 using the recently developed Moulin Shape (MouSh) model. The MouSh model requires additional subglacial baseflow to simulate an accurate diurnal range of head oscillation. We hypothesize that this additional baseflow is the result of strong network connectivity with other moulins through a channelized subglacial drainage system, potentially supplemented by basal or non-local, upstream inputs. Additional work is necessary to accurately characterize moulin positions and life cycles, and to determine whether the observed annual formation and abandonment is widespread. Such characterization would improve the simulation of moulin inputs in models. In addition, further knowledge of the shape of moulins around the equilibrium head elevation would improve englacial storage parameterization in subglacial hydrological models and aid predictions of coupling between meltwater and ice motion under future melt scenarios. Finally, this work suggests that the connectivity of the subglacial network needs further study, to improve our understanding on how local and non-local drivers influence subglacial water pressures and ice sliding.
